I have always been bad at sexing plecos. I can only do it one of two ways with any reliability. The most reliable method is to vent them. That is to have them put out their tube so you can see its shape. males have a pointed tube while females have a more rounded blob-like tube. She has to pass eggs and he only needs to let out a squirt and the tube shapes reflect this fact.

Body shapes and features help but are not 100% reliable by any means.

I can also generally sex mature adults based on behavior as long as this does not involve large numbers in the same tank. Males claim caves and raise eggs/fry. Females may shelter in caves but do not claim them. In a tank with a pair you will see the male in the cave a lot of the time and the female will hide under wood or rocks most of the time. Of course if you can catch them in the act of spawning it is easy. She will leave the cave after laying and he tends the eggs.

Because I am older and my eyesight isn't what it used to be, I find it is easiest for me to determine sexes by taking pictures and then looking at them on my PC screen, It is a lot easier to see the features when you can enlarge the image. You images are not of a quality where enlarging them still shows clear details.